Core barrel retriever



06h22, 1935, 1 N, KSENHOLT 2,018,414

CORE BARREL RETRIEVER Filed May ll, 1934 2 Sheets-Sheet l y PZ 42.

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f6 f A la? w f5 IV 1 Ing I @f l if* ,29" "a ig L Hf@ -ff .1:2 52/ IM 5.1' j |NvENToR d/ys/B/Se/ya/ BY c www i5 ATTORNEYS Oct. 22, 1935. J. NQoKsENHoLr CORE BARREL RETRIEVER 2 sheets-sheet? Filed May 11, w34

u, `umnffffffwlffff n J2. INVENTOR v n W d W w 5 5, r A@ VV 4l :1. 5 2A n z5@ Jg. 5 77 a i@ 7 454.@ .J w fv f. 7 a a u f QQ, 5. a 5 6 n\v fr J* ,8 1 m L Lmw event the latter cannot be asians @UEE BREL RE'REWR .lens N. Okse'olt, Shreveport, lila., assigner ci one-fourth to Everett Bi. lilland, one-smith to @harles E. Emery, one-sixteenth to Frank T.

Gibbes, and one-sixteenth to Edgar ils.

liilands,

Sr., all o Shreveport, lLa. Application May lill, i934, Serial No. 725.1%

The invention relates to mechanism for withdrawing or retrieving core barrels from operative relation within a drill head and stem and it has for its principal object the provision of means for disconnecting the retrieving tool from the core barreLwhen the latter, for any reason, cannot be withdrawn from the drill head and stem.

A primary feature of the invention consists in providing either the core barrel member or` the retrieving member with a-movable spindle which is adapted to automatically engage the other of said members when the retrieving member is lowered into the drilling stem for withdrawing the core barrel, means being carried by the spindle and movable relatively thereto upon movement of the members toward each other for eiecting disengagement of the retrieving member and core barrel, in the event the c ore barrel cannot be withdrawngfrom the drill stem.

Another feature of the 'invention consists in providing the spindle, which is carried by either the core barrel member or the retrieving member, with a sleeve which is adapted to move relatively to the spindle when the members are moved toward each other, so as to disconnect the retrieving member from the core barrel, when the latter cannot be withdrawn from the well.

A further feature of the invention resides in providing the core barrel with a spindle which is movable upwardly with theretrievlng member, the spindle being provided with means which is movable upwardly therewith andfis adapted to be supported in an elevated l positionso as to eiect disengagement of the retrieving member from the spindle upon movement of the Imembers toward each other.

A still further feature in providing the retrieving member with a. movable spindle having releasing means for disconnecting the member from the cor'e barrel, in the withdrawn, the retrieving member being provided with means for moving the releasing means relative to the spindle to cause disengagement of the members.

A still further and more specific feature of the invention consists in providing suitable means, suoli as' a frangible-pin, for preventing relative movement of the spindle and the member with which it is associated, which movement causes the releasing means to assume an operative position, until after the-spindle hasbeen subjected to a force greater than that required to withdraw the core barrel from the drill stem.

Other and more specic features of the invention residing in advantageous forms, combinations and relations ofparts will hereinafter appear and be pointed out in the claims.

In the drawings, illustrating diiierent embodiments of the invention,

Figure 1 is a vertical sectional view of the of the invention consists (Cl. ESS-JW) upper part of the core barrel, a portion oi the spindle being in elevation. l

Figure 2 is a vertical sectional View, on a reduced scale, othe drill head, a part of the drill stem and the lower portion of the core barrel.

Figure -3 isa vertical sectional view, of the retrieving tool or member. p y

Figure 4 is a vertical sectional View showing the retrieving mber connected to the core barrel, the releasing means having been moved by the spindle into operative position.

Figure 5 is an enlarged bottom View of the ysleeve constituting the releasing means.

Figure 6 is a fragmentary side elevational view of the lower portion of the sleeve.

` Figure '7 is a vertical sectional view of a modi- 15 ed form of the invention showing the relative position of the parts of the mechanism prepara-- tory to being connected together. p

Figure 8 is a vertical sectional view of the `mechanism illustrated in Figure '7, showing the relative position of the parts preparatory to effecting release of the retrieving member from the core barrel.

Figure 9 is avertical sectional view of the mechanism ef Figure '1, illustrating the relative position of the parts in the act of releasing the retrieving member from the core barrel.

Figure 10 is a vertical sectional view corresponding to Figure 7 of still another embodiment of the invention.

Figure l1 is a sectionalview taken on line ll-Il of Figure 7.

Figure 12 is a sectional view taken online .l2- I2 of Figure 8. o

is a continuation in part of application Serial No. 668,862, for Core barrel retrievers, filed May 1,.1933, which latter application is a division of application Serial No. .617.464, for Core barrel construction, filed June 15, 1932.

Referring more particularly to the drawings; I indicates a drill head carrying cutting bits 2, the head being secured to the lower end of a drill stem, generally designated by the reference numeral 3. Disposed Withinthe drill stem and normally extending beyond the drill head is a. core barrel l having a. tubular body portion 5 which is adapted to be operatively connected to the drill stem by any suitable means, such as a bushing 6, which is fully described in my copending application Serial No. 617,464 and which forms no part of the present invention.

This application The upper portion er the tubular body s erv the core .barrel is provided with a cage-like cou-v pling 1 carrying a ball check 8, the top of the coupling being closed by a plug-like member 9 and being connected to an upper tubular sections duced diameter to provide an interior shoulder I I. Connected to the upper end of the tubular member I0 is an additional tubular section I2 which has an interior diameter slightly greater than the adjacent portion of section I0.

Slidably mounted in the upper end of the core barrel within the tubular member I0 is a spindle or the lilre I3 having an enlarged portion I4 near its lower end to afford a shoulder I5, which is adapted to engage the shoulder I I on the interior of member I0, when .the spindle is raised or moved upwardly relatively to the core barrel. The upper portion of the spindle is provided with a reduced cylindrical section I6 to form a shoulder II and the outer end of the spindle, which normally projects beyond 'the tubular member I2, is provided with a flanged head of greater diameter than the adjacent portion ofi/the spindle and preferably conoidal in form for cooperation with a retrieving tool, such as a standard overshot.

l Slidably mounted on the reduced section I6 of the spindle is a sleeve I9, the upper portion of which is of slightly larger external diameter than the body portion, as indicated at 20. 'I'he sleeve normally occupies the position lshown in full lines in Figure 1 with its lower end engaging the shoulder il! oi. the spindle, so that, when the lower end oi the spindlerests upon the plug-like member il, the upper portion-of the sleeve is preferably disposed just within the upper rim of the tubular member I2. The function of the spindle is to afford connection between the retrieving member and the core barrel to permit the latter y to be withdrawn from the drill stem after the taking of a core, and the function of the sleeve is to eect disconnection oi the retrieving member from the spindle, in the event it is impossible to release the core barrel from its connection with the drill stem. .A suitable retrieving member for engaging the spindle is illustrated in Figure 3 and comprises a member 2l attached to the end of a cable 22, which cable extends through the drill stern to the top of the latter, as will be understood by those skilled in the art. Member 2l is connected with a plug-like member 23 which has a longitudinal bore to receive a stud 24 projecting upwardly from a coupling member 25, the upper end or the stud carrying an anti-friction bearing member 26v held in place by a nut 2l threaded onto the upper end oi' the stud, whereby the coupling is swivelled to the plug 23 and member 2|. 'I'he lower portion o1' the coupling 25 is connected by a tubular member 28 with the head of an overshot, which, as stated, may be of standard form and comprises a tubular section 29 having an enlarged cylindrical chamber in which dogs or detents 30 are secured by screws or studs 3|, the upper portion of the dogs being urged inwardly toward the axis of the overshot by springs 32. The lower end oi.' the tubular member 29 is preferably ared as at 33 to permit the conoidal head I8 of the spindle lI3 to pass into the interior of the tubular member 29 and move upwardly therein until the lower end of the retrieving member engages the upper end of the core barrel, at which time the spindle will have passed upwardly into the retrieving member a suilicient distance to enable the dogs 30 under the iniiuence of the springs 32 to engage under the iiange or shoulder formed by the lower portion of the head I8. This operation will connect the retrieving member with the core barrel, so

that, when the latter is released from operative association with the drill stem, it may be withfrangible pin ,countered in withdrawing the latter.

eiect 'release of the core barrel, it is highly 5 desirable to release the retrieving member from the core barrel and withdraw itfrom the drill stem prior to withdrawal of the latter, as other- Wise the cable connected to the retrieving member must be cut at each section of the drill stem to enable the latter to be disconnected as the stem is being withdrawn.

The release of the retrieving tool from the core member is eiected by the sleeve I9, which is raised by the upward movement of the spindle I3 15 after it has been engaged by the retrieving member and the latter elevated a short distance by the cable 22 -in the initial movement of the retrieving member to withdraw the core barrel. Upward movement of the spindle and consequently the sleeve relativelyto the core barrel is arrested when the shoulder I5 of the spindle engages the shoulder II of the core barrel. The sleeve is supported inits elevated position by any suitable means, such es a spring detent 34, 25 which may advantageously be clamped between sections I 0 and I2 of the core barrel and is adapted to pass into engagement with one of the :dat shoulders formed on the lower end of the sleeve by cutting away segments, as indicated'at 30 dogs 30 will be in frlctional engagement with the exterior of the sleeve i9 and the enlargedhead 40 of the spindle will be resting upon the upper end l oi the sleeve; Upward movement of the retriever at this time will cause the spindle and sleeve to correspondingly move due to the frictional engagement between the latter and the dogs until the shoulder I5 ofthe spindle again engages shoulder tI of the core barrel, at which time the retriever will move upwardly relatively to the spindle and sleeve and, since the external diameter of the sleeve is slightly greater than the maximum external diameter of the spindle head, the dogs will not operatively engage the latter and the retrieving tool is thus free to be withdrawn from the drill stem.

The sleeve I9 is supported in its elevated position by the spring detent 34 until the drill stem, together with the core barrel, is removed from the drill hole to effect release of the core barrel. After withdrawal of the c ore barrel in this manner', the sleeve may be caused to assume the position indicated in full lines in Figure 1 by being partially rotated, thus forcing the spring detent 34 out oi' engagement with the shoulder 35 and onto the adjacent peripheral surface of the sleeve. l Y

If desired, the spindle I3 may be connected to'the tubular section I0 of the core barrel by a 36, which is `suilciently strong to prevent relative movement between the spindle and core barrel, in the event diiliculty is not ven- On the other hand, however, the pin is sufficiently weak that, in the event the core barrel cannot be released !rom the drill stem and a force greater than that normally required to remove the core aciers .to release the retrieving member from the spindle. By connecting the spindle and core barrel by a frangible pin, it is unnecessary to reset the releasing sleeve each time the core barrel is withdrawn from the drill stem by the retrieving tool, but those skilled in the art will readily appreciate that the sleeve is just as effective to release the retriever from the core barrel, when the pin is omitted, the only diierence being that, if the pin is not used, it becomes necessary to reset the sleeve each time the core barrel is withdrawn from the drill stem in the usual manner. f I

In the modified form of the invention illustrated in Figures 7 to 13, inclusive, the retrievyD ing member 3l is provided with a spindle 38 which corresponds to and functions in somewhat the same manner as the spindle I3 which is carried by the core barrel in the form oi the invention illustrated in Figures l to 6, inclusive; while the core barrel is provided with a tubular section 39 which corresponds to and functions in substantially the same manner as the tubular section 2li of the retrieving member in the rst described form of the invention. Y

The retrieving member 3i comprises a socket d@ attached to the end of a cable di, which, as will be readily understood, is employed for raising and lowering the retrieving member within the drill stem. The socket'member Il@ is connected by a plug i2 to a tubular sectionfl having a longitudinal bore which is of vreduced di-y ameter at its lower end to provide a shoulderif. The spindle 38, which is disposed within inember it and is of sufficient size that its lower end will always project beyond the latter, is provided at itsupper end with an enlarged head i5 to afford a shoulder te which is adapted to engage the shoulder it to limit downward movement of the spindle relatively to the retrieving member. The lower portion oi the spindle is provided with a reduced cylindrical section dl which forms a shoulder di', and the lower end thereof is iitted with a head i8 of larger diameter than the adjacent portion of the 'sp'ndle and preferably conoidal in torni.

Slidably mounted on the'reduced portion il of the spindle is a sleeve de', the lower portion of which, as indicated at 5u, is of slightly larger diameter than the body portion. The sleeve is normally adapted to be disposed within the tubular section (i3, being supported in that position by spring fingers or detenta 5| which are secured in any suitable manner to a tubular extension 52 of the member d3. While the spring lingers 5l may function to only support the sleeve ls, they may be made suillciently strong to also sup port the spindle 38, since` downward movement. o! the spindle relatively to the sleeve is prevented by the shoulder 41 thereof engaging the upper end of the sleeve. However, instead of relying on the spring ngers for not only supporting the sleeve but also the spindle in elevated position, as shown in Figure 10, the spindle may be supported by a frangible pin 53 which is adapted to extend within registrable openings in the head 45 of the spindle and the walls of the tubular section 43, as shown in Figure-7. 1

The tubular section 39 may be fastened onto the upper end of the core barrel 56 by any suitv able means, such as a plug or the like 55. Disposed within the uppenportion of the tubular section t@ are dogs' which are pivotally mounted at their upper ends on pins or studs 5l, 5 the lower portion of the dogs being normally forced inwardly by springs 58. The upper end of the tubular section 39 above the pivoted dogs 5S is of rsomewhat smaller inside diameter than the body thereof but it is preferably dared, as indicated at 59, to readily permit the head t8 oi the spindle to pass into the tubular section when the retrieving member is lowered.A Downward movement of therretrieving member continues until the spindle bottoms within the tubular section 39, at which time the head of the spindle will have moved sumciently to permit the dogs to spring back into ,engagementwith the reduced portion dirci the spindle above the head 48, whereby the .dogs function to connect the rre- 20 trieving member and core barrel.

After the retrieving member has been thus connected to the core barrel, upward movement of the former will induce `similar movement oi' the latter;r In the eventthe spindle is connected 25 to the retrieving member by 'a rangible pin,v the spindle and sleeve will remain in the same relative positions as indicated in Figure 'l during withdrawall of the core barrel from the drill x stern, it, of course, being understood that the so irangible pin is sumciently strong to support the extra Yweight oi the core barrel. However, ii the spindle is not connected to the retrieving member by a frangible pin, the member, upon being elevated, will move upwardly with respect as to the spindle and sleeve until shoulderfi of the spindle is engaged by shoulder it of the tubular section 33, at .which time the spindle will be raised with the retrieving tool. llt will be ob; served that during the time the retrieving memgo ber is moving upwardly relatively to the spindle and sleeve, the spring fingers di are caused to slide along the exterior oi the sleeve and shortly before the shoulders lli and ld come into en-` gagement, the fingers .pass from engagement with, 5 the sleeve. As soon as this occurs, the sleeve, ofr course, is free to slide downwardly on the .spindle into a position similar to that shown'in Figure 8. However, the weight of the sleeve is not sufficient to force the dogs 5t from engagement with the head it of the spindle and thus disconnect the retriever and core barrel. y

Should it be found impossible for some reason. to release the core barrel from operative association with the drill stem, the sleeve which, under 55 .ordinary working conditions is functionless, is

operated to eect disengagement of the retriever from the core barrel, so that the retriever may be withdrawn from the drill stem. ln the case where the spindle is connected to the retriever by 60 a :rangible pin sumcient force, such, for example, as ve thousand pounds, is imparted to the retriever to shear the pin. As soon as the pin is sheared and the retriever is moved upwardly relatively to the spindle, the parts of the mechanism 35 will assume the position indicated in Figure 8.

The sleeve td is now in a position such that it is capable of functioning to release the dogs 56 from engagement with the head 48 of the spindle. This is accomplished by lowering the retrieving 'mem- 70 ber with respect to the core barrel to bring the lower end of the spring ngers 5I which normally occupy positions closely adjacent the spindle, into engagement with the upper end of the sleeve, so that by continuing to .lower the retrieving mem- 75 ber, the fingers force the sleeve downwardly and thereby move the dogs 56 outwardly f rom engagement with the spindle into the positions indicated in Figure 9. Subsequent raising of the retrieving member will cause it to move upwardly relative to the spindle until the shoulders 46 and 44 are brought into engagement. at which time the sleeve and spindle also moveupwardly free of the core barrel, as the sleeve prevents the dogs 56 from again moving into operative engagement with the spindle. In the event the spindle is not connected to the retrieving member by a fran'gible pin, release of the dogs 56 from the spindle 39 is effected in substantially the same manner just described. The only difference between the cperation of the retrieving member provided vwith a frangible pin and one not so provided is that, in the latter case, the sleeve is, upon connection of the retrieving member and core` barrel, immediately brought into a position such that it is capable of being operated to eiect release of the dogs, while, in the former case, it is necessary to shear the pin before the sleeve is brought into operative position.

From the foregoing, it will be appreciated that simple and efficient means has been provided for withdrawing a core barrel from the stem and, in the event the core barrel cannot be withdrawn,

l for effectingy release of the retrieving member from the core barrel .so that the retrieving member may be-withdrawn from the drill stem and thus preserved for future use. Those skilled in the art will appreciate that the invention is not limited to use in connection with corebarrels and that it is equally well suited for use in connection with the removal of a great variety of devices from Wells in general.

What I claim is 1 1. In combination,` a core barrel member adapted to be associated with a drill stem, and a retrieving member .adapted to be lowered into said stem for connection to the core barrel to withdraw thelatter from the stem, one of said members having a movable spindle and the other of said members having mechanism adapted to automatically engage said spindle when the retrieving member is lowered into `the drill stem, and means carried by the spindle for disconnecting said members when the core barrel cannot be withdrawn from the stem, said means being movable by the spindle into a position whereby upon movement of the members toward each other said/means will force said mechanism from eng'agement with the spindle.

2. In combination, a core barrel member adapted to be associated with 'a drill stem, and a retrieving member adapted to be lowered into said stem for connectionto the core barrel to withdraw the latter from the stem, one of said members having a movable spindle and the other of said members having mechanism adapted to automatically engagesaid spindle when the retrieving member is lowered into the drill stem, releasing means'canried by the spindle for'disconnecting said members when the core barrel cannot be withdrawn from the stem, said spindle having a portion cooperable with the releasing means to move the latter into operative'position upon movement of said members in opposite directions, said releasing means being relatively movable with respect to said mechanism upon subsequent movement of the members toward each other for forcing said mechanism from engagement with the spindle.

""XB. In combination, a core barrel member adapted to be associated with a drill stem, and a ref:

trieving member adapted to be lowered into the drilling stem for connection to the core barrel to withdraw the latter from the stem, one of said members having a movable spindle provided with a flanged head and the other of said members being provided with detent means automatically engageable with said iianged head when the retrieving member is lowered into the drill stem, a sleeve carried by the spindle for disconnecting said members when the core cannot be withdrawn, said spindle having a portion cooperable with the sleeve to move the latter into operative position upon movement of said members in opposite directions, said sleeve being relatively movable with respect to said detent means upon subsequent movement of said members toward each other for forcing the detent means from engagement with said anged head.

4. In combination, a core barrel member adapted to be associated with a drill stem, and a retrieving member adapted to be lowered into the stem for connection to the core barrel to withdraw the latter from the stem, one of said members carrying a movable spindle and the other of said members having mechanism adapted to automatically engage the spindle when the retrieving member is lowered into the stem, means for releasing the spindle from said mechanism when the core barrel cannot be withdrawn from the stem, said releasing means being movable into position to effect the release of said mechanism upon relative movement of the spindle and its carrying member, and means normally preventing relative movement of the spindle and its carrying member until after the spindle has been subjected to a force greater than that normally required to withdraw the core barrel.

5. Mechanism for retrieving a core barrel from a. drill stem including a core barrel provided with a movable spindle adapted to be automatically connected with a retrieving tool when the latter is lowered into the drill stem, means slidably mounted on the spindle adapted to disconnect the later from the retrieving tool when the core barrel cannot be withdrawn from the drilly stem, said means being movable upwardly by the spindle, and means for supporting said slidable means in an elevated position whereby the latter is adapted to effect disengagement of the spindle from the retrieving tool upon lowering of the latter.

6. Mechanism for retrieving a core barrel from a. drill stem including a core barrel provided with a movable spindle adapted to be automatically connected with a retrieving tool when the latter is lowered into the drill stem, avsleeve movably vmounted on the spindle adapted to disconnect the latter from the retrieving tool when the core barrel cannot be withdrawn from the drill stem, said spindle having a portion cooperable with the sleeve for moving the latter upwardly therewith upon corresponding movement of the retrieving tool, and means for supporting said sleeve in elevated position whereby the latter is adapted to'eiect disengagement of the spindle from the releasing means disconnect the latter from the retrieving tool when the core barrel cannot be withdrawn from the drill stem, said member being movable upwardly by the spindle, and a spring detent for supporting said member in elevated position whereby the latter is adapted to effect disengagement of the spindle from the retrieving tool upon downward movement of the spindle relatively thereto. y

8. Mechanism for retrieving a core barrelfrom a drill stem including a core barrel provided with a movable spindle adapted to be automatically connected withthe retrieving tool when the latter is lowered into the drill stem, means adapted to disconnect the retrieving tool from the spindle when the core barrel cannot be withdrawn from the drill stem, said means being movable into operative position by movement of the spindle relatively to the core barrel, and means preventing the. spindle from moving said rst named means into operative position until after the spindle has been subjected to a force greater than that required to normally barrel.

9. Mechanism for retrieving a core barrel from a drill stem including a core barrel provided with a movable spindle adapted to be automatically connected to a retrieving tool when the latter is lowered into the drill stem, a sleeve movably mounted on the spindle and adapted to be moved upwardly by the latter into position to disconnect the retrieving tool from the spindle when the core barrel cannot be withdrawn from the stem, and a frangible pin preventing movement of the sleeve by the spindle into operative position until after the spindle has been subjected to a force greater than that normally required to withdraw the core barrel from the stem.

10. Mechanism for retrieving a core barrel from a drill stem including a retrieving tool provided with a movable spindle adapted to be automatically connected with a core barrel when the tool is lowered into the drill stem, means slidably mounted on the spindle adapted to disconnect the latter from the core barrel when the barrel cannot be withdrawn from the drill stem, and means carriedv bythe tool and engageable with the slidable means to force the latter downwardly relatively to the spindle for disconnecting the spindle from the core barrel.

ll. Mechanism for retrieving a core barrel from a drillstem including a retrieving tool provided with a movable spindle adapted to be automatically connected with a core barrel when the tool is lowered into the drill stem, releasing means slidably mounted on the spindle and movable downwardly disconnect the latter from 'the core barrel when the barrel cannot be withdrawn from the drill stern, and means for supporting said releasing means in an elevated inoperative position.

l2. Mechanism for retrieving a core barrel from a drill stem including a retrieving tool provided with a movable spindle adapted to be automatically connected with a core barrel when the tool is lowered into the drill stem, releasing means slidably mounted on the spindle adapted to disconnect the latter from the core barrel when the barrel cannot be withdrawn from the drill stern, means for supporting said releasing means in an elevated position, and means for moving said downwardly relatively to the withdraw the coreably mounted on spindle for the core barrel.

13. Mechanism for retrieving a core barrel from a drill stem including a retrieving tool provided With a movable spindle adapted to be automatically connected with a core barrel when the tool is lowered into the drill stem, releasing means slidably mountedl on the spindle adapted to disconnect the latter from the core barrel when the barrel cannot be withdrawn from the drill stem, said spindle being adapted to move said releasing means downwardly relatively to the tool for causing said means to assume an operative position, and means carried by the tool for subsequently moving the releasing means relatively to the spindle to effect release of the latter from the core barrel. l

14. Mechanism for retrieving a core barrel from a drill stem including a retrieving tool provided with a movable spindle adapted to be automatically connected with a core barrel when the tool is lowered into the drill stem, means for disconnecting the spindle from the core barrel when the barrel cannot be withdrawn from the drill stem, said means comprising a sleeve slidably mounted on the spindle and being movable downwardly therewith relatively to the tool, and means carried by the tool for supporting the sleeve and spindle in an elevated position.

15. Mechanism for retrieving a core barrel from a drill stem including a retrieving tool provided with a movable spindle adapted to be automatically connected with a core barrel when the tool is lowered into the drill stem, releasing means slidably mounted on the spindle adapted to disconnect the latter from the core barrel when the barrel cannot be withdrawn from the drill stem, andmeans carried by the tool for forcing said releasing means downwardly relatively to the spindle for releasing the latter from the core barrel, said last named means being also adapted to support the releasing means in an elevated inoperative position.

16. Mechanism for retrieving a core barrel from a drill stern including a retrieving tool provided with a movable spindle adapted to be automatically connected with a core barrel when the .tool is lowered into the drill stem, means adapted to disconnect the spindle from the core barrel `when the barrel cannot be withdrawn from the drill stem, said means being movable into operative position upon relative movement of the spindle and tool, and means preventing relative movement of the spindle and tool until after the spindle has been subjected to a force greater than that normally required to withdraw the core barrel.

1'1` Mechanism for retrieving a core barrel from a drill stem including a retrieving tool provided with a movable spindle adapted to be automatically connected with a core barrel when the tool is lowered into the drill stem, a sleeve slidthe spindle and movable upon relative movement of the spindle and tool into a position for disconnecting the spindle from the core barrel when the barrel cannot be withdrawn from the stem, and a frangible pin preventing relative movement of the spindle and tool until after the spindle has been subjected to a force effecting release of the latter from greater than that normally required to withdraw 70 

